Taps drip. It's inevitable, like death and taxes. Traditional taps seal using a rubber ring screwed down over the end of a metal pipe. Sooner or later the rubber is going to go hard, split or just wear away and it will no longer seal. Then water seeps through, and the tap starts dripping. Left alone the problem gets worse as the water wears away the valve seat. Then you'll have to either re-grind the valve seat(Do you own a valve seat re-grinder? Who would?) or replace the tap. Tedious in either case. But, it need not happen. Many taps now use ceramic discs.
Method of Operation Instead of creating a seal by forcing a rubber washer onto the end of the water feed pipe, they use two ceramic discs each with matching slots in them. These are held over the end of the water feed pipe. The lower disc doesn't move while the upper disc is turned over the lower disc by the tap head. Water will only flow when the upper and lower slots match up.
Advantages There are a number of benefits to this arrangement. The most obvious is that ceramic discs are much harder than rubber and much more resistant to erosion by water seepage. Hence they have a much longer life before needing replacement. Additionally, because the water flows between the two discs, the discs erode not the metal of the valve. Also, because of the way the discs are arranged, the taps go fully on with only one quarter of a turn and tap needs only light pressure to operate. This light action has the advantage that they are easy to operate with the back of the hand if your hands are dirty and for people with restricted movement.
Where they are Used The ease of operation and the long life mean that most good quality sink mixer taps have been made using ceramic discs for a while, but basin taps with ceramic discs are surprisingly less common. The more use a tap gets, the more attractive the use of ceramic disc technology becomes. This is doubly true in hard water areas, which can be murder on traditional taps.
Everything has it's downside, and there are cons to ceramic disc taps. They do eventually wear out and are more expensive than old style taps and are not suitable for very low water pressure. Unusually, many of the manufacturers seem to use standard sizes, so getting a replacement is often straightforward. Because taps on basins can be either handed or not not, one can't always be sure which way to turn each tap on, this can be annoying! Lastly, unlike traditional style taps, which take a number of turns to be on full, you may easily turn the water flow on far more than meant. The unexpectedly vigorous water flow and splashing can cause water going everywhere, including over your clothes. Not Good!